I've always used plastic canisters - I tried metal ones, but didn't like them - too insecure for me - i.e. I was never sure whether the cap is tight enough.
As I said, never had any problems with plastic ones - and those 6 or 7 I had previously got reloaded more times than I can remember (dozens of times each,at least!). No scratches, no problems whatsoever. Much easier to load and handle than metal (USED!) ones. I must stress that I tried metal used cans - not the ones designed for reloading, but ordinary color film metal cans, which I opened using bottle opener 🙂
I understand that you can buy metal canisters designed for reloading, though I never tried those.
You can use discarded metal ones from the photo-labs without opening them by simply joining the bulk film to the remaining piece of original film still protruding from the container, using sticky tape, as described on many Web sites on bulk loading.